Project Summary/Abstract: Adolescent obesity continues to be a major public health concern due to the increased risk of developing chronic diseases, including, but not limited to, type 2 diabetes. Thus, strategies are vitally needed that target weight management and glycemic control to reverse the obesity epidemic and prevent and/or delay serious health complications in young people. The daily consumption of breakfast has been touted as an essential part of the diet to prevent and/or treat obesity. While breakfast was once thought to be `the most important meal of the day', this notion has recently been challenged due to the paucity of existing causal evidence. In addition, interest in the study of breakfast and weight management has highlighted the importance of macronutrient content, particularly increased dietary protein at breakfast, as a critical factor. Pilot data has illustrated reductions in body fat mass and improvements in glycemic control following the daily consumption of high protein breakfasts over a short period in overweight adolescents. However, it is unclear as to whether these effects would occur over the long-term and what mechanisms-of-action contribute to the improvements in these health outcomes. Aim 1 will determine whether a causal link exists between breakfast, particularly one rich in dietary protein, and weight management in young people. To accomplish this, 150 overweight, habitual breakfast-skipping adolescents will complete the following long-term randomized, tightly-controlled breakfast trial. Participants will be randomly provided with high protein breakfasts (350kcal; 34% protein (30g protein), 40% CHO, and 26% fat); isocaloric normal protein breakfasts (350kcal; 11% protein (10g protein), 63% CHO, and 26% fat); or will continue to skip breakfast for 6 mo. Baseline, 3, and 6 body weight, body composition, and free-living glycemic control will be assessed. In addition, daily intake, with particular focus on evening snacking behavior, will also be measured at baseline, 3, and 6 mo. Aim 2 will identify the appetitive, hormonal, and neural signals by which a protein breakfast modulates ingestive (i.e., eating) behavior and weight management. To address this aim, a sub-set of the 150 (n=75) will complete 10-h testing days during baseline, 3, and 6 mo. Repeated assessments of perceived appetite, satiety, and food cravings along with appetite- regulating hormonal responses (i.e., plasma ghrelin, GLP-1, PYY, and HVA (the primary dopamine metabolite)) will be measured throughout the day. On a separate day, post-breakfast and pre-dinner functional (fMRI) brain scans will also be completed to identify neural activation to food stimuli in cortico-limbic brain regions known to modulate food motivation, reward, and cravings. Aim 3 will identify specific appetitive, hormonal, and neural signals as strong predictors of ingestive behavior and weight management. The measures collected in Aim 2 will be analyzed in combination with food choice, daily intake, weight loss, and reductions in body fat following the 6-mo interventions. Collectively, this project will provide novel evidence testing the consumption of a high protein breakfast as a dietary strategy to combat obesity in young people.